Streep will play Mary Louise Wright, the mother of Alexander Skarsgard's character who was killed off during the HBO show's Emmy-winning first season. According to The Hollywood Reporter, Wright is "a woman who is concerned for the well-being of her grandchildren following her son Perry's death" and comes to Monterey "searching for answers."
Season 2, which was already greenlit for seven episodes, is also rumored to feature Bonnie's (Zoe Kravitz) parents.
HBO previously said the season will explore the "malignancy of lies, the durability of friendships, the fragility of marriage and, of course, the vicious ferocity of sound parenting. Relationships will fray, loyalties will erode... the potential for emotional and bodily injury shall loom."
Streep, Reese Witherspoon and Nicole Kidman are the only cast members confirmed to return to the drama so far, while the rest of the stars renegotiate their contracts.
"Big Little Lies" won eight Emmys and four Golden Globes for its first season.